When selecting the audio output destinations (headphones, FP headphones,
multichannel output), unnecessary I2S channels are digitally muted to
avoid invalid signal levels on the other outputs.
Signed-off-by: Roman Volkov <v1ron@mail.ru> Signed-off-by: Clemens Ladisch <clemens@ladisch.de> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>